1. Field of the Invention
The present invention relates to a method of and apparatus for scanning the surface of a workpiece.
2. Description of the Related Art
Fully integrated machine probing systems are known for scanning workpiece surfaces for example from machines tools made by the Companies Rambaudi, Maho and Jobs.
In such known systems a probe and the machine control system are connected so that the machine control system instructs the machine to drive along a predetermined vector. The probe readings and the machine scale readings are continuously fed back to the control system, and at regular intervals the control system latches the probe readings, calculates a vector for continued probe movements, and sends a new command to the motor drive system of the machine.
Where a machine has no fully integrated probing system for scanning, it is desirable to have a "plug-in" probing system which can be retro-fitted to the machine to enable it to carry out scanning operations.
One attempt to produce a "plug-in" scanning package for a machine has been made by the Le Moine Company of the U.S.A. This system makes use of the fact that the control system of a CNC machine tool has a positional feedback loop which includes the machine motor drives, the machine scales and a controller, whereby a cutting tool can be driven accurately through a machining cycle. The system provides a scanning probe and an additional computer (PC) which issues commands to the machine controller motor drives. The feedback signals from the positional feedback loop of the machine to the controller are tapped to provide readings of the instantaneous probe position to the PC, and the probe output signals are also passed to the PC.
While this system achieves the objective of enabling machines hitherto without a scanning capability to be given a "plug-in" scanning option, it requires a costly process of tapping into the machine's control architecture to provide the feedback signals to the PC, and an expensive program card for the PC to enable it to receive the feedback signals both from the machine and the probe and to act on these signals to produce the drive commands to be sent to the machine controller.
An object of the present invention is to produce a retrofit package for a machine tool which provides the machine tool with a scanning capability in a relatively inexpensive manner.
Another object of the invention is to provide a machine tool with a method of, and apparatus for, scanning which operates via a computer separate from the machine controller without the need for feedback signals from the machine.